In the prior art, when a narrow cloth strip to be used as a safety belt, a seat belt or a sling is subjected to a treatment such as dyeing, heat treatment, scouring or finishing, a plurality of cloth strips run continuously in a side-by-side manner, i.e., in parallel with, through a series of processes, which normally start the supply of greige fabric and include scouring, dyeing, rinsing, drying, heat-setting and the application of a surface agent.
The above technique for treating cloth strips has various problems as follows:
(1) If the running speed of cloth strips arranged in parallel to each other is increased to reduce the treatment time in the respective process, it is necessary to lengthen the running section, which naturally results in an increase in the respective unit size. Such an increase in the unit size causes an uneven temperature distribution in the unit. Particularly, when such temperature difference occurs in the dyeing process, a difference in hue or color density appears in the respective cloth strips running in parallel. PA1 (2) When the cloth strips run parallel to each other, there is a problem of lack of running stability wherein some of the cloth strips may be in a slack state or meander due to a tension variation. If the unit size is enlarged, this tendency would be increased. PA1 (3) Recently there has been a remarkable trend toward smaller lots of diverse sorts and/or multicolor products. Using to the conventional parallel running system, the working efficiency is low because it requires time for each exchange of the dye solution, each alteration of the webbing tension and each change of a process condition such as temperature or speed.
To solve the above problems, the present inventors proposed a treatment method as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 1-34845 "Apparatus for Shifting Running Position of Narrow Width Fabric" wherein a single cloth strip runs along a spiral path in a predetermined treatment zone.
According to this proposal, it is possible to keep a longer length of cloth strip in the predetermined treatment zone, whereby it is possible to shorten the treatment time and remarkably increase the running speed. Thus, the productivity has been improved compared with the conventional parallel running system. In addition, differences in hue, color density, elongation or others have been reduced to stabilize the product quality
However, it has been found that there are problems remaining still unsolved, which are as follows:
First, a problem relating to a rubber roller used in the treatment of this type will be discussed. In the prior art, a nip roller device or mangle wherein the surface of roller is formed of rubber is used in an introduction/withdrawal roller device, for introducing/withdrawing a cloth strip, provided at the entrance and exit zones of a unit used for carrying out a thermal treatment, on a narrow cloth strip having a narrow width thereof, such as scouring, dyeing, resin treating or heat-setting. The cloth strip is nipped between a plurality of rollers brought into contact with each other, and introduced into or discharged from the respective unit driven by these rollers.
In the prior art, most of the rubber rollers used for such treatments are made of known rubber materials, such as natural rubber, SBR, NBR, CR (chloroprene rubber), IIR (butylic rubber), FPM, urethane rubber or silicone rubber. Since such rubber rollers are usually disposed near to the entrance and exit zones for the main thermal treatment zone, they are directly influenced by the high temperature in the treatment zone and if the rubber rollers have a low resistance to heat, they are damaged by heat in a short period.
Further, the temperature rise of the rubber roller provided in the exit part of the thermal treatment zone is considerable because the heat-treated cloth strip is withdrawn while being pressingly nipped by the roller surfaces, whereby the deterioration of the rubber is accelerated.
Particularly, in the above system wherein the cloth strip runs along a spiral path, the cloth strip passes over one portion of the introduction/withdrawal roller provided in the thermal treatment zone at a high speed. In a thermosol setter, for example, for carrying out the color development and heat-set, the surface temperature of a cloth strip at a position immediately after the thermal treatment zone is about 180.degree. C. which means that the surface temperature of the withdrawing roller portion supporting the cloth strip also rises to about 180.degree. C. Since the running speed is about 72 m/min, the rubber roller rapidly wears and becomes unusable within a few hours if a conventional rubber roller is used.
Accordingly, it is necessary to frequently replace the rubber roller with new one in the prior art, which results in the complicated replacing operation and an increase in the production cost.
If the thermal treatment is a dyeing or color development process, the rubber roller tends to be contaminated with dyestuff which rubs off onto the dyed product to cause a color change or contamination thereof. To solve such a problem, it is necessary, when a plurality of cloth strips are dyed, that the dyeing order is determined so that a lighter color dye precedes a darker color dye. Also the rubber rollers must be frequently rinsed and, if the contamination of rubber rollers cannot be removed by rinsing, it is necessary to replace the rubber rollers after a period of two or three months, which results in reducing the working efficiency and increasing the production cost.
Next, problems with conveying rollers for the cloth strip used in the thermal treatment zone of this type will be described below.
In the prior art, a plurality of cloth strips run through the heated treatment zone, in parallel, on a plurality of conveying rollers arranged, with a distance therebetween, in the upper and lower areas of a bath. Namely, according to this system, the cloth strips sequentially pass over the respective conveying rollers from the entrance zone to the exit zone.
Therefore, when the cloth strip contracts due to heat, the rotational speed of the respective conveying rollers can vary throughout the thermal treatment zone from the entrance zone to the exit zone, even in a passive manner, in response to a variation in the running speed of cloth strip caused by heat contraction.
However, in the case of the above spiral running, there is an inconvenience in the conventional conveying rollers, as follows:
Usually, in the heat treatment of a cloth strip, the cloth strip gradually contracts due to heat during the first 90 seconds. Particularly, in the thermal treatment in which the cloth strip runs along a spiral path to give the strip a high elongation, it is necessary to allow the cloth strip passing the thermal treatment to contract during the contraction period.
That is, when a cloth strip is introduced into a treatment zone having a capacity for holding the cloth strip for about 180 seconds, and is subjected to a thermal treatment while running along a spiral path, it is necessary to run the cloth strip faster in the first half of the running zone, in which the cloth strip remarkably contracts, than in a second half in which almost no contraction occurs. Otherwise, the contraction generated in the first half of the zone is disturbed.
Actually, even in the first half of the contraction zone, it is necessary to precisely regulate the running speed in response to the contraction of the cloth strip.
In the thermal treatment apparatus wherein a plurality of conveying rollers used in the conventional parallel running system are provided, each formed integrally with a rotary shaft, all the cloth strips running on any one of conveying rollers are driven at the same speed because all portions of this roller have the same rotational speed. Therefore, if the conveying roller of this type is used in the spiral running system, lengthwise portions of the same cloth strip running adjacent to each other and having different contractions may be inhibited from freely contracting due to the friction with the roller, whereby a product having high elongation is not obtainable.
As stated above, the problems to be solved by the present invention, the contamination and lack of durability of rubber rollers, the contamination and lack of durability of introduction and withdrawal rollers in the spiral running system, and the structure of the conveying rollers provided in the thermal treatment zone, remain unsolved in the conventional spiral running system.